Components of high-temperature mechanical systems, such as, for example, gas-turbine engines, operate in severe environments. For example, the high-pressure turbine blades, vanes, blade tracks and blade shrouds exposed to hot gases in commercial aeronautical engines may experience metal surface temperatures of about 1000° C., with short-term peaks as high as 1100° C.
Components of high-temperature mechanical systems may include a Ni- or Co-based superalloy substrate, a ceramic substrate, or a ceramic matrix composite (CMC) substrate. Some ceramics or CMCs possess excellent high temperature mechanical, physical and chemical properties, and may allow gas turbine engines to operate at higher temperatures than gas turbine engines having superalloy components.